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Drafting or slipstreaming is a technique where two vehicles or other moving objects are caused to align in a close group reducing the overall effect of drag due to exploiting the lead object’s slipstream. Especially when high speeds are involved, as in motor racing and cycling, drafting can significantly reduce the paceline’s average energy expenditure required to maintain a certain speed and can also slightly reduce the energy expenditure of the lead vehicle or object.

It’s the evolution of the sport. By the 80s the cars were easily doing over 200mph laps at Daytona and Talledega. The dangers soon became obvious and to slow them down they were required to place a restrictor plate on the intake manifold. This restrictor plate is still used today though the size has varied.

Restrictor plate racing is basically full throttle all the time. If your car isn’t part of the draft you can’t go fast because you move too much air. A few years ago with the last generation Cup car the drivers found that two car drafts were faster and could pull away from the pack. So it ended up with all these two car, tandem, drafts all over. The newest Cup car doesn’t do this as well. It’s still working for the Nationwide cars.

There is some pre-race maneuvering between people who are
not already betrothed to another driver, as to who will pair up &
as to which will be draftee & which the drafter. Apparently, there
is a noticeable tactile ‘click’ when you find exactly the right alignment.
By previous legal agreement, none of this symbolizes anything.

They were doing it intentionally. That’s the ‘cleverly titled’ strategy known as push-drafting (also called bump-drafting) – seriously, that’s its name. I don’t know the reason making contact is required, but it is claimed to be a more efficient method of drafting. It seems to be used less now, with the current generation of car design: it is much easier to cause the front car to spin and cause extremely high-speed accidents – which, much to my surprise, apparently is not the intent of Nascar racing at all.

I tried the same thing once with our cycling group, although it was not intentional: the guy on whom I was drafting suddenly had a thigh cramp and slight right fucking down. Word: road bikes, with 21 and 23mm tires, don’t take to bump drafting. Much skin and flesh was left on the pavement.

And yes, sometimes the car behind DOES physically push the one in front. That commonly results in a spinout, however.

Yes it does – with the car designs used in 2013. In 2012 and earlier, spinouts did not occur as often – rarely, if both drivers were aware and knew what was going on. That’s why it came to be so common.

Yeah, Dean, bump drafting will not work if what’s bumping are two tires moving in opposite directions. Bump drafting is much more stable when done with car bumpers that are moving very little relative to each other.

Theoretically, if the two cars were solidly joined together, they would be significantly faster than single cars – something like a tandem blowing off the front of a paceline. The closer the second car is to the first, the less drag it encounters. If the car in front is going at 100%, the car directly behind is going at 70-80%. If the two cars were in contact, then that extra power that is not being used by the second car can be transferred to the leading car, moving the tandem faster. The situation is probably not stable for a long period of time due to a lack of coordination between the drivers.

“Yeah, Dean, bump drafting will not work if what’s bumping are two tires moving in opposite directions. Bump drafting is much more stable when done with car bumpers that are moving very little relative to each other.”

I did realize that, I hope you understand :) – it was an apparently poor attempt at humor on my part. Touching tires, even the slightest of grazings, with two bicycles is never a good idea.